Generally, lighting systems are used for horticultural applications in greenhouses or other environments where living organisms are to be irradiated with light, e.g. photo-bioreactors, to support plant growth. When developing new horticultural systems, one of the most important goals is the reduction of the total cost of ownership (TCO).
In the art, different documents report on the influence of pulsed light on the growth of plants, e.g. US 2004/0109302 A1. The described studies show that pulsed light (frequency, duty cycle), compared to continuous light, has a positive effect on energy consumption but no negative effect on plant growth. It is believed that a plant's pigment cannot directly absorb a second photon after absorption of a first photon. So, pulsed light decreases the TCO due to reduced power consumption, thereby increasing the overall efficiency of the system. A light source that can be easily pulsed is a light emitting diode (LED). The efficiency of today's LEDs (measured in micromole/J) is getting close to or is already above that of state-of-the-art high pressure sodium lamps. In addition, the emission spectra can be tuned to the absorption spectra of the pigments. A problem, however, is that drivers for LEDs do not offer a high efficiency, a high power density, high reliability and galvanic isolation at the same time.
Another problem relating to high pressure sodium lamps for horticultural applications is that they typically generate light in the green/yellow spectrum. However, the absorption spectra of most common pigments are in a different frequency range.